Method for the pyrolysis of diacyl cyanides



Patented Dec. 22, 1953 12,663,726 ti-cruel)" roe Til-it PYnoLY'sr's *OF "GY-ANIDES an er isfiurai ga tijh ras ianc lt 1 The B. Goodrich (Company, New Yo'rl, N. Y.,

a cert-oration ofTNv'v York 1 .N'o Drawing. Application May '7, 1952-,

Serial No. 286,598

. 1 This invention relates to -a method for pyrolyaingdiacyl cyanides whereby vinylidene cyanide (also known as 1-,1-dicyano ethylene) or one of its homologs is obtained, and pertains more particularly to thepyrolytic deacyloxa-tion of diacyl cyanides in the presence or an inert diluent mate a V It is disclosed in U. S. Patent 2,476,270 that the-diacyl cyanide, l-acetoxy-Ll-dicyano ethane, can-be pyroly-zed at temperatures in the range of 406 (Lite 750"; G. to givemonomericvinylidene cyanide, an extremely valuable polymerizable material which is especially useful in the preparation of polymer-sandinterpolymers suitable as syntheticfibers, synthetic resins and plastics.-

However, unless the process as described in the patent is carried out at reduced pressures, preferably from 2 to 50 mm. of mercury, the yield of the desired vinylidene cyanide is not as high as is desirable and carbonization of the pyrolysis tube occurs to a considerable extent. This dependency on reduced pressure for optimum re: sults is' quite dissatisfactory for a number of other reasons. For example, the production and Y maintenance of suc'ha vacuum involves the he stalla't'ionpf expensive equipment and-the-neces' sity'for-c'lose operational control, both "of which add materially to the initial cost and continued up keep-df the pyrolysis plant. Also, reduced pressure l makes necessary on a large scale the use of-a-large-pyrolysistube and/or ahigh tern perature" and-limits severely the amount er pres sure drop through the pyrolysis tube. These conditions in turn lead to a pronounced temperature drop across the gas film at the tube interface with attendant over-cracking along the tube walls and reduced stability of the pyrolysis product. Additionally, reduced pressurepyrolysi-s requires the use of very low temperatures for condensation of the pyrolysis vapors, this factor again adding to the cost. of a pyrolysis-plant. As-

a result of these disadvantages, the ,process. specifically described in U. S. Patent 2,476,270 is not as well suited for practical commercial usage as is desired.

Accordingly, it is an object of the present invention to provide aprocess whereby l-acetoxy- 1,1-dicyano ethane, as well as other diacyl cyani'des', may be readily and economically pyroiyze'd with high yields f desired product and without operational difliciiltis, at atmospheric pressure or even at pressures above .atmo'spheric. V d

It is a second object. of thisinvention to provide approc'ess whereby diacyl .cyanides can-be '7 claims. (01.216044653) pyrolymd to give improved yields of fiction vrylidene cyanideor its honorees, rerd 6f theoperating pressure. Qther objects bea'fi-T parent from the description which 'fol d it has now been discovered that the above and other objects may ,be readily accompus ed ay carrying out the pyrolysis of diaylcyanides in the presence of a-diluent material to the diacyl cyanide and th pyfc'il thereof When such inert d'i'l'ue t utilised, the pyrolysiscan be cari'i mospherig, xpressur'e 'to give goodconv, on Q the diacy-l cyanide to aicnciner antlhflgh fields of; monomeric vinylidene cyanide oriits' honifol Moreover, many other advanta es 6" "th duced pressure pyrolysis or an auncsp e'iic pr 51- surepyrolysisuti grno inert diluent taned. For examp e, the use of afiji'fiert .dllu increases greatly the stability of the cr pyrolysis product (this being :very lfflpfo'rta h we teime i r n. is u-ite difiicult to station) and decreases overcracliing at the ga layer adjacent the that i'n'teffa'c. Moiovi} when-the inert diluent is a liq id ,at robin i'iinf-- perature-andat-atmospheric 151'] sure the met: ing ;point of the diacyi cyanide ed to .tli pyr'olyzer is'lowered as" is the dew oint of the yrolysisproduct yapdrs, both of wiuehare quite desirable especially no I the standpcrnt' econoi'n'y nd'easecf- 6 tion ilhe pyrdlysisof diacy'hyanldes the process of .th

R an'acyloxy radical; preferablycon-f tailii"--fr0m2 O 6 carbcmatcma-and R iS'j'hy-t drogen or a row airy-l radical-' 'preferablyscon tainma rrcm 0 -4 carbon atoms; WhenfR'is h roam there is: produced vinylidene cyanide and aboxylicacid whereas whenR' islower.1al-

cyanide arhoniolog'.therebfzof-ztheiiormulaf H l It r e pyri'ciysis an .rccvry pi tire productscan belcarfiedijolitlins era-1 difi,

e present invention j proceeds ways. One preferred method, whereby the desired product is obtained in highest yield with greatest efiiciency, consists in adding an inert liquid diluent to the diacyl cyanide, vaporizing the resulting mixture, and passing the vapors at atmospheric pressure through a heated pyrolysis tube, preferably of brass or stainless steel, wherein there occurs decomposition of the diacyl cyanide into monomeric vinylidene cyanide or a homolog thereof, a carboxylic acid, and other unidentified products. The pyrolysis product vapors are then directed into a quench system where the vapors are condensed, preferably by direct contact with a large liquid flow of cold pyrolysis product containing the inert liquid diluent as is more fully disclosed in copending application Serial No. 286,496, filed May '7, 1952. After flash distillation to remove any solid which may be present, the liquid condensate can be utilized without further purification in the preparation of homopolymers and interpolymers of the monomer since the carboxylic acid and any other impurities present in the condensed pyrolysis vapors have no appreciable efiect on the polymerization reaction; in fact, the inert liquid diluent provides a very convenient polymerization medium.

v,Alternatively, the monomeric vinylidene cyanide or homolog can be recovered from the crude pyrolysis product in substantially pure form by distillation, by crystallization from a solvent such as toluene, or by treating the pyrolysis product with a conjugated diolefin such as butadiene or cyclopentadiene which reacts with the monomer to form. a solid substituted cyclohexene which can be separated from the carboxylic acid and other impurities and pyrolyzed at temperatures in excess of about 400 C. to give monomeric vinylidene cyanide or homolog and the conjugated diolefin. Also if monomeric vinylidene cyanide is being prepared it can be recovered by utilizing its tendency to autopolymerize and causing it to polymerize as formed as by pouring the liquid product into water to speed up the polymerization, after which the solid polymer can be easily separated from the liquid materials by filtration or decantation. The polymerized vinylidene cyanide can then be depolymerized by pyrolysis,

preferably at temperatures of 170 C. to 250 (3., to give monomeric vinylidene cyanide, a process described more fully in U. S. Patent 2,535,827.

' When the inert diluent is a gas at room temperature and atmospheric pressure, it is preferably introduced into the diacyl cyanide vapors before the vapors enter the pyrolysis tube.

The temperature at which the pyrolytic decomposition takes place may be varied widely without seriously affecting the conversion of diacyl cyanide to monomeric vinylidene cyanide. In general, however, temperatures in the range of 400 C. to 750 (1'. should be utilized, with optimum conversions being obtained when temperatures in the range of 475 C. to 575 C. are employed. As noted above, operation at atmospheric pressure is preferred'but reduced pressures may also be utilized with attendant improvements over the process as carried out inthe absence of an inert diluent.

The diacyl cyanide feed rate, that is, the num- 'ber of parts of diacyl cyanide introduced into the pyrolysis tube per unit of time, may also be varied widely without appreciable efiect on the conversion. However, it has been found that the quantity of inert diluent utilized does have a substantial effect on conversion. Accordingly,

4 it is desirable that about 8 to 12 moles of inert diluent be utilized per mole of the diacyl cyanide in order that highest yields of monomeric vinylidene cyanide will be obtained.

The material which is utilized as a diluent in accordance with the present invention must be a substance which is inert toward both the diacyl cyanide and the monomeric vinylidene cyanide or homolog under the conditions of pyrolysis, that is, it must neither react with nor afiect said compounds at any stage of the pyrolysis process. Included among the substances which are inert toward diacyl cyanides and monomeric vinylidene cyanide and its homologs are compounds which are liquids at room temperature and atmospheric pressure and also compounds which are gases under such conditions. For example, one particularly preferred class of compounds which are successfully employed as inert diluents in the pyrolysis of diacyl cyanides is the liquid aromatic hydrocarbons or halogen substituted aromatic hydrocarbons such as benzene, o, m, or p-toluene, o, m, or p-xylene, monochlorobenzene, dichlorobenzene, trichlorobenzene and the like. Inert diluent gases which may be utilized include nitrogen, hydrogen, helium, methane, ethane, propane and other inert gases. It is to be understood, of course, thatthe inert diluents disclosed above do not represent all of the inert substances which can be utilized, but the materials disclosed are indicative of the types of substances which can be employed.

The process of this invention is especially useful for the pyrolysis of diacetyl cyanide (l-acet- However, other diacyl (3N RA -om t wherein R is an acyloxy radical and R is a lower alkyl radical, such as l-propionoxy-1,l-dicyano propane, l-acetoxy-l,1-dicyano butane, l-propionoxy-l,l-dicyano ethane, l-butoxy-1,1-dicyano butane, l-amyloxy-l,1-dicyano ethane, and the l ke, also may be pyrolyzed by the process of this invention to give monomeric vinylidene cyanide or a homolog thereof, and a carboxylic acid. l-propionoxy-l,l-dicyano propane, for example, gives methyl vinylidene cyanide,

H ?N i=i CH: CN

and propionic acid.

The following examples are intended to illustrate more fully the pyrolysis of diacyl cyanides in the presence of an inert diluent. They are not, however, intended to limit the invention, for there are, of course, numerous possible variations and modifications. In the examples all parts are by Weight.

Example I A series of pyrolysis reactions is carried out by admix ng l-acetoxy-l,1-dicyano ethane with inert liquid diluents and pumping the resulting solution into a heated glass pyrolysis tu'be packed. with glass helices and maintained at atmospheric pressure. Thepyrolysis product vapors are condensed and collected in a cooled receiver and the liquid pyrolysis product analyzed for monomeric Moles dilu- Feedrate i Percent enttper. {portal-am.- gconversxon Dmmmw mole .l-ace tony-1,, Temperaof, d acyl. toxyd; l-dicyano turer G. eyauideto' lt-dicyand 'etha nelper'r .{vinylidene ethane. minute. cyanide Benzene=-.... f. 5.0. 0.265. 450' 30.6 D'O I QIO 01171 5G5 80. 1 gggf g fgfig 14.5 0310'4- 51m 85. 5 H" i gg; 10.3 0.140 520 8018 103101 03165": 3 500. i 82.5 10.0 0.239 500, 79.6 H)? 0. 320 I. 525 83.5 10. 0 0. 320 550 79. 6

Example II" Monomeric vinylidene cyanide. is pr n ire s y passingzvapors. ofv l.ace.toxyr hilz-dicyanu. ethane at atmospheric pressure through a glass pyrolysis tube which is heated to a temperature of 650 C. A mixture of methane, ethane, and propane, serving as an inert diluent, is passed through the pyrolysis tube together with l-acetoxy-l,1-dicyano ethane vapors. The crude pyrolysis product vapors are condensed in a cooled receiver and the liquid condensate distilled to give a 75.5% yield of substantially pure monomeric vinylidene cyanide.

In addition to being useful individually, the liquid inert diluents and gaseous inert diluents can be utilized in combination in carrying out the pyrolysis of diacyl cyanides in accordance with the present invention. In the following Example III, the use of inert liquid-gas diluent compounds is shown.

Example III A series of pyrolysis reactions is carried out by admixing parts of 1-acetoxy-1,1-dicyano ethane with 40 parts of dry monochlorobenzene, heating the mixture to a temperature just below the boiling point thereof, bubbling an inert diluent gas into the melt below the surface thereof and allowing the gas vapors to carry the mixture into a heated pyrolysis tube maintained at atmospheric pressure. The pyrolysis product vapors are then condensed and collected in a cooled receiver and'the liquid pyrolysis product analyzed for monomeric vinylidene cyanide content. The inert gaseous diluent utilized, the pyrolysis temperature and per cent yield of monomeric vinylidene cyanide are recorded in the following table:

Percent Pyrolysis yield of Inert diluent gas temperamonomerle ture, C vinylidene cyanide Pro one 580 64. 7 Nitx ogen 580 72. 8 Mixture of methane, ethane and propane" 550 76. 6

6 ferred on a plant scale; the process of this; 1m: vent'ion involving the use of an: inert diluent. also; results in improved yields: at lower pressures as is shown in the followingExample IV.

Eazample IV A series of pyrolysis reactions is carried out 'in the same generalxma'nn'er. as;Example Iiwith the exception: that reduced pressure" maintained by means" of" a vacuumpump. In eaclr reaction "40 grams of facetbxy-lal-dibyano ethane is vaporized by heating, with or without a" diluent; and is then" passedi into the pyrolysis apparatuswhere the vapors are heated to 650 Cf The pressure maintained", the inert diluent? used iffany', the; durationof the pyrolysis reacthin:v the yield of monomeric. vinylidene: cyanide the condensed pyrolysis" product anditsistability (err pressed as. the number" of minutes" required formation; of polymer when the liquid pyrolysis: product is allowed to" stand at at given temperature) are recorded in the followi'ngtablef" Percent Pres- 33%} yield of sure, Inert diluent run vinyli- Stability of product mm. dene cyanide 70 73.6 32 min. at 70 0. 35 88.0 29 min. at 70 C. 150 ..d0 5O 43. 0 13 min. at 70 C. 14 Methane gas, 19-25 50 82 36 min. at 100 C.

ccJmm. 200. Methane gas, 27-37 69. 2 68min. at C.

calmm. 50 Trichlorobenzene, 45 72. 7 23 min. at 100 C.

40 grams. 150 do 68.7 36 min. at 100 C. 200 do 90 60. 2 93 min. at 100 0. l5 'lrichlorobenzene, 70 70.5 min. at 100 C.

40 grams+methane, 19-27 cc./min. 200. Trichlorobenzene, 53.3 76 min. at 100 C.

40 grams+methane, 32-43 cc./min.

The data show that higher yields are secured at generally comparable reduced pressures and that the product possesses greater stability against polymerization when the pyrolysis is conducted in presence of an inert diluent in accordance with this invention.

Example V wherein R is an acyloxy radical and R is a member of the class consisting of hydrogen and lower alkyl radicals, at a temperature of 400 C. to 750 0., and in the presence of at least 8 moles D3 y g 9.

of an inert volatile organic diluent, said diluent being free of conjugated diene groups and homopolymerization accelerating groups for the ethane to methyl pyrolysis product thereby to produce a pyrolysis product comprising a compound of the structure i CN wherein R has the same meaning as above.

2. The method of claim 1 wherein the diacyl cyanide is l-acetoxy1,l-dicyano ethane and the pyrolysis product comprises monomeric vinylidene cyanide.

3. The method of preparing monomeric vinylidene cyanide which comprises pyrolyzing 1- acetoxy-Ll-dicyano ethane at atmospheric pressure at a temperature of 400 C. to 750 C. and in the presence of an inert diluent selected from the class consisting of liquid aromatic hydrocarbons and liquid halogenated aromatic hydrocarbons, there being present at least 8 moles of said compound per mole of the said l-acetoxy- 1,1-dicyano ethane.

4. Themethod'of claim 3 wherein the inert diluent is benzene; r

5. The method of claim 3 wherein the inert diluent is chlorobenzene.

6. The method of claim 3 wherein the inert diluent is a mixture of benzene and xylene.

7. The method of preparing monomeric vinylidene cyanide which comprises pyrolyzing 1- acetoxy-l,1-dicyano ethane at atmospheric pressure, at a temperature of 400 C. to 750 C. and

in the presence of a gaseous saturated aliphatic hydrocarbon.

' ALAN E. ARDIS.

' References Cited in the file of this patent UNITED STATES PATENTS Ardis et a1. Dec. 26, 1950 

1. THE METHOD WHICH COMPRISES PYROLYZING A DIACYL CYANIDE OF THE STRUCTURE 